MT63 Modes

General Description

MT63 is an Orthogonal Frequency Division Multiplexed (OFDM) mode consisting of 64 parallel carriers each carrying
part of the transmitted signal. The tones are differential BPSK modulated. MT63 employs a unique highly redundant
Forward Error Correction system which contributes to its legendary robustness in the face of interference and fading.

The tones have synchronous symbols, and are raised cosine modulated. The mode requires a very linear transmitter.
Over-driving leads to excessive bandwidth and poorer reception. The mode is unpopular with many operators
because of the excessive bandwidth used.

The mode is very tolerant of tuning, as most software will handle 100Hz mistuning. The mode was designed
by Pawel SP9VRC.

Coding and Character Set

The ASCII-128 user interface is mapped to 64 tones via a Walsh-Hadamard function (rate 7/64), and uses an interleaver
to spread each character across 32 or 64 symbols. Character mapping is direct (via the coding function and interleaver,
there being no scrambler or gray coder.

There are three modes, which are scaled in all dimensions (baud rate, spacing,
typing speed), and two interleaver options (short and long). One shortcoming of the mode is that robustness is compromised
with the short interleaver, and latency (delay between overs) is unacceptably long with the long interleaver. For example,
with the default mode the latency is 12.8 seconds.

Operating Parameters

Mode

Symbol Rate

Typing Speed1

Duty Cycle2

Modulation

Bandwidth3

ITU Designation4

MT63-500

5.0 baud

5.0 cps (50 wpm)

80%

64 x 2-PSK

500 Hz

500HJ2DEN

MT63-10005

10.0 baud

10.0 cps (100 wpm)

80%

64 x 2-PSK

1000 Hz

1K00J2DEN

MT63-2000

20 baud

20.0 cps (200 wpm)

80%

64 x 2-PSK

2000 Hz

2K00J2DEN

Notes:
1. WPM is based on an average 5 characters per word, plus word space.
2. Transmitter average power output relative to a constant carrier of the same PEP value.
3. This is the "Necessary Bandwidth" as defined by the ITU.
4. A summary of the ITU Designation system can be found at http://en.wikipedia.org/wiki/Types_of_radio_emissions
5. Default and normal calling mode (long interleaver).